The present invention relates to a hydroponic installation for growing plants, in which the roots are constantly immersed in an aqueous nutrient solution.
It is known that a plant's capacity for absorbing water depends on the water's degree of saturation with dissolved oxygen, not merely with dissolved air, in the area about its roots.
It is obvious that, unless the plant absorbs water it absorbs no nutrients.
There are, furthermore, periods when the roots need to release gases, such as carbon dioxide (CO.sub.2) and ethylene.
Since the aim is to dissolve a gas--oxygen in this case--in water, the method currently most used in aquariums, for example, consists in blowing air into the water, which is a poor method.
This is because each air bubble, which contains 21% oxygen, as in the atmosphere, has but a small surface area through which its oxygen has to be able to diffuse into the volume of water, namely, the water that surrounds the bubble, which is enormous in relation to the volume of the bubble.
However, in the HCI process, which is the subject matter of the invention, this enormous volume of water is broken up into small droplets, each being surrounded by an enormous volume of air in relation to the volume of the droplet. In other words, the physical conditions in this process are completely reversed.
Consequently, since gases seek a state of equilibrium (a fundamental law of physics), oxygen, abundant in air, will easily diffuse through the surface of the water droplets which contain little or no oxygen.
During the growth of the plant, its roots release into the water carbon dioxide (CO.sub.2) or ethylene, which causes the concentration of these gases in the droplets to exceed that of the ambient air. Hence, these gases will easily be able to leave the water droplets to diffuse into this ambient air. It is in this that the HCI gas exchange process consists. Of the two saturations, oxygen saturation is by far the most important, because it is more difficult to achieve economically. This difficulty is all the greater when the temperature of the air and of the water is higher, that is, in spring, which is precisely the season when the plants' oxygen demand is greatest, because they are in their full growth activity and are laden with fruits.
It is in such conditions that the other systems prove to be insufficient, resulting in the death of a great number of roots and the deterioration of the plant itself, with the possibility that this devastating sickness may extend to all the other roots.
It is also known that roots gripped in a solid support can be damaged mechanically by the latter, and since the tissue of the plant, hurt by this support or otherwise, is held in place, it can decompose to create a disease that will destroy all of the roots in existing hydroponic systems, both static and circulating.
Two methods will be described for injecting nutrient substances, one of them using laser-drilled holes, the other using individual nozzles, both permitting the delivery of the necessary nutrient solution in the form of fog. The laser method requires a higher distribution pressure and a pump of a larger size for very large installations permitting the development of roots from plant cuttings, but it can also be of inestimable value for the root growth of difficult varieties of plants. The nozzle method requires less pressure but operates with a greater rate of flow, which makes it quite recommendable for plants such as tomatoes which need a long period of growth (up to one year), which results in a substantial increase both in growth and in the destruction of the mass of the roots. The greater flow of the injector system results in the accelerated removal of destroyed root tissues, assuring an environment free of diseased roots.
Various patents have already been filed in this field, including the European Patent Nos.:
0,010,737 of Dec. 1, 1982
0,052,264 of Jan. 2, 1986
both of which relate to a hydroponic apparatus comprising a tank with removable cover containing an aqueous nutrient solution and an air space between the surface of the latter and the cover in which openings are created, each able to receive different devices for holding these plants firmly in a vertical position.
In the first patent, the aeration of the solution is performed by a central device driven, either constantly or intermittently, by an electric motor. This vertical-axis device includes, on the one hand a horizontal disk revolving in the air space, and on the other hand a tube for aspirating the nutrient solution, injecting the latter directly onto the disk whose marginal shape combined with its rotation produces the flow of the nutrient solution into the air space in the form of very small droplets forming a fog.
In the second patent a tubular overflow enabling the level of the nutrient solution to be regulated is connected to a well-known system outside of the tank, including, among other things, a circulation pump, a water supply, a system for regenerating the solution with mineral salts, filters, and a by-pass, the nutrient solution being injected under pressure into the tank through one or more tubular, substantially horizontal ramps, half immersed in the solution, through a series of holes aiming the solution upwardly toward the cover, such that the air space is filled with a fog of nutrient solution descending continually into the solution and constantly being replaced with other amounts of injected solution.
Experience has shown that these two patents did not give the expected results.
The objective of the present invention is to improve the yield of such hydroponic cultures by eliminating all dead plant waste by the rapid elimination of damaged or deformed portions of roots, constituting ideal environments for the development of disease.